High speed, high density, low power die interconnect system

ABSTRACT

A system for interconnecting at least two die each die having a plurality of conducting layers and dielectric layers disposed upon a substrate which may include active and passive elements. In one embodiment there is at least one interconnect coupling at least one conducting layer on a side of one die to at least one conducting layer on a side of the other die. Another interconnect embodiment is a slug having conducting and dielectric layers disposed between two or more die to interconnect between the die. Other interconnect techniques include direct coupling such as rod, ball, dual balls, bar, cylinder, bump, slug, and carbon nanotube, as well as indirect coupling such as inductive coupling, capacitive coupling, and wireless communications. The die may have features to facilitate placement of the interconnects such as dogleg cuts, grooves, notches, enlarged contact pads, tapered side edges and stepped vias.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.13/865,604 filed on Apr. 18, 2013, which is a continuation of U.S.patent application Ser. No. 13/169,353 filed on Jun. 27, 2011 and issuedas U.S. Pat. No. 8,426,244, which is a divisional of U.S. patentapplication Ser. No. 11/459,081 filed on Jul. 21, 2006 and issued asU.S. Pat. No. 7,999,383, the entireties of which are herein incorporatedby reference.

FIELD OF THE INVENTION

The present invention relates generally to integrated circuit packagingand more particularly to interconnecting die.

BACKGROUND OF THE INVENTION

Integrated Circuit (IC) packages, chips (sometimes called die), andother devices have evolved into very dense packaged structures.Semiconductor miniaturization has resulted in the development of verylarge scale integrated circuit (VLSI) devices with millions of activeand passive components. These devices are typically encapsulated in aprotective package providing a large number of pin-outs for mounting orinterconnection to external circuitry through a carrier substrate suchas a printed circuit board or other higher-level packaging.

The semiconductor industry is well over 60 billion dollars a yearmarket. Improved fabrication technologies have lowered cost whileincreasing functional power thereby revolutionizing the electronicmarketplace. The ability to put more and more functionality and higherperformance is generally made possible by repeatedly shrinking featuresizes. However, as the more and more functionality and performancecharacteristics are included in these chips, the limits of currenttechnologies and methodologies are approached. There are a number ofissues and trends that are becoming readily apparent. For example,package temperature issues are exacerbated by a number of factorsincluding static power and lowered junction temperatures due to smallerfeature sizes and lowered thresholds. Also, hot spots within the chipsare exacerbated by the active elements being buried so deeply beneaththe conducting layers and contacts.

In the formation of integrated circuits, a number of active and passivesemiconductor devices are formed on each of many die on a wafer, such assilicon. The fabrication technology for integrated circuits has vastlyimproved yields such that large arrays of electronic circuits on manydie are produced on a single semiconductor wafer. In a typical die, twoor more silicide layers and up to eight metallization layers, eachseparated by a dielectric layer, are currently used to interconnectamong the active and passive elements to form the individual circuitsand to interconnect among those circuits to form the die. They are alsoused to provide bonding pads at the top of the die. For example, TexasInstruments has a 65 nm process that uses eleven (11) copper conductinglayers plus two polysilicide layers for a total of twenty-seven (27)conducting and dielectric layers.

Typical interface schemes for integrated circuit packaging include PinGrid Array (PGA), Ball Grid Array (BGA), and Land Grid Array (LGA), PGApackages use a two-dimensional array of pins directly connected bysoldering or inserted into through-hole pads in a Printed Circuit Board(PCB). BGA packages have a two-dimensional array of conductive pads,such as balls, bumps or pillars, and are mounted by soldering the padson the package to corresponding surface pads on the mount side of thePCB. LGA packages have an array of metal stubs and are mounted to thePCB in a clamp with a compressible interposer material placed betweenthe package and the PCB.

For illustrative purposes, the description herein will focus somewhat onthe most common package, the BGA. The BGA bond pads of the semiconductordie are sometimes connected to the printed circuit board via conductors,either by direct contact in a flip-chip orientation through conductiveballs, bumps or pillars or, by intermediate connector elementscomprising wire bonds, or TAB (flexible circuit) connections. Morecommonly they are connected inside a package which in turn is solderedto the PCB. In addition, as ball sizes shrink, they are less tolerant ofthe already worsening planarity problems.

One of the well-known problems with having the connection balls on theactive surface of the die is the planarity required of the die. Theproblem is compounded as the number of mask levels increase toaccommodate the latest demand for processors and memory. The furtherlayers exacerbate the planarity problem and make the die connection moredifficult. Another problem associated with the dense packaging is thatthe fanin/fanout of a given ball is limited to either a single fanin ora single fanout. One of many deleterious effects of this property isthat only one element can be placed on a bus unless another delay stageis introduced. Typically, many three state elements are “hung” on a bus,and only one such element is active at any one time. The third state,the high impedance state, of the inactive elements ensures that theyneither charge nor discharge the bus.

With respect to the formation of BOA structures, these structurestypically require the die to be flipped upside down hence the name “flipchip”. A problem with flipping the chip upside down is that allpossibilities of monitoring chip behavior in-situ are eliminated.Integrated circuit (IC) dies typically connect to the substrate withinthe IC package using either wire bond or Flip-Chip technology. Flip-Chipbonding is normally used for high pin count IC dies, and the pins on theFlip-Chip die are called bump pads. As with the package arraytechnologies, there is a matching pattern of pads on the packagesubstrate. Interconnect on the package substrate is typically used toconnect the pads on the substrate (connected directly to the IC die) tothe pins, pads, or stubs on the surface of the package that getsinserted, soldered, or pressed to the PCB.

A further problem with using the current flip chip techniques arisesfrom a combination of bringing the interconnects to the top of the diein combination with the large number of layers. The connection to/fromthe underlying layers must be brought to the top of the die forconnection to a connection ball. Current chips have six to eightmetallization layers plus two polysilicon layers, and each of theseconducting layers is separated from adjacent conducting layers by adielectric layer. Thus, a signal on the lowest conducting layer may haveto go through as many as nine conducting layers and ten dielectriclayers, including one on the top surface, in order to reach the topsurface and be connected to an interconnect ball.

In order to traverse from each conduction layer through the interveningdielectric layer to connect to an adjacent conduction layer generallyrequires a stepped via to minimize and avoid step coverage problems. Astepped via is a hole whose cross-section is larger on one end than onthe other. It has a contact on both conducting layers, and a short pieceof interconnect to route to a via to go to the next upper or lowerconduction layer. This process is repeated for each such signal line foreach conducting layer until the top is reached. Both the vias and thecontacts are considerably larger than the width of the line; thus aconsiderable area is utilized just for the interconnects to the balls onthe top surface of the chip.

It is well-known that as the capacity and speed of many integratedcircuit devices, such as dynamic random access memories (DRAMs) haveincreased, the number of inputs and outputs (I/Os) to/from each die hasincreased, requiring more numerous and complex external connectionsthereto and, in some instances, requiring undesirably long traces toplace the bond pads serving as I/Os for the typical die in communicationwith the traces of the carrier substrate.

A related problem with the current techniques is the interconnectivitybetween dies. Signals that travel to other dies must traverse not justupwards in one die, but may also travel further upwards if the seconddie is on top of the first die. The signals may also traverse downwardinto a second die to reach the desired point on a given conduction layerin the second die. Thus, for example, the signal may traverse upwardsthrough many conduction and dielectric layers to reach the top diesurface and go through a ball, a bonding pad, or other connectionstructure on the first die. After a connection to a second die, thesignal would then be similarly routed downwards from the top surface ofthe second die to the desired layer in the second die. Thus, forexample, a given signal could traverse about thirty-eight (fifty-four inthe case of the 65 nm process of Texas Instruments) conduction anddielectric layers and their associated vias plus two conduction balls,bonding pads, or other connection structure. And, each of the contactlayers adds resistance that, in combination with the total lengthtraversed by the signals, may impact signal quality, speed, noisemargin, bus skew, slack and setup/hold times, rise and fall times,potential spike generation and signal cancellation and makes timingconvergence and other design and verification aspects difficult andsometimes limits upper clock frequencies.

Thus, such a tortured path impacts both speed and signal integrity. Itis well known that interconnect delays are often much greater than gatedelays below feature sizes of roughly 0.5 to 0.35 micron. Traversingsubstantial numbers of interconnect layers on two or more dieconsiderably exacerbates the problems of timing convergence, layout, andarchitecture. Attempts to minimize these problems typically placerestrictions on the layers regarding the manner in which signals cantravel among these layers. These restrictions increase the alreadydifficult layout and hinder designer creativity. They also sometimesforce restrictions on the architecture of the chip.

Long path lengths also add significantly to the capacitance seen by thesource and slow the signal down. Moreover, as line widths continuallydecrease, 22 nanometers currently in development, the number of“squares” and hence the resistance of the line in a given length of lineincreases by about the same factor as the decrease in line widths. Thisthen increases the resistance seen by the driving source, again by aboutthe same factor as the decrease of the line widths, all else being thesame.

Furthermore, the increased line resistance adds to often alreadystrained power usage and dissipation while making it more difficult tomake bus signal elements and slave clock signals track their respectivefunctions.

In addition, as higher speed IC assemblies operate at lower operationalsignal voltages, noise problems also become problematic. Mutualinductance results from an interaction between magnetic fields createdby signal currents flowing to and from a packaged IC die through leadsor traces, while self inductance results from the interaction of theforegoing fields with magnetic fields created by oppositely-directedcurrents flowing to and from ground. Signal propagation delays,switching noise, and crosstalk between signal conductors resulting frommutual and self inductance of the conductive paths contribute to signaldegradation.

While lead inductance in IC packages has not traditionally beentroublesome, the increasing signal frequencies of state-of-the-artelectronic systems have substantially increased the practicalsignificance of package lead or trace inductance. For example, at suchfaster signal frequencies, performance of IC die using extended leads ortraces for external electrical connection is slower than desirablebecause the inductance associated with the elongated conductive pathsrequired slows changes in signal currents through the leads or traces,prolonging signal propagation. In addition, digital signals propagatingalong the leads or traces are spreading out causing the signalcomponents and signals themselves to disperse. While mild dispersionmerely widens the digital signals without detrimental effect, severedispersion can make the digital signals unrecognizable. In addition,reflection signals propagating along the leads or traces as a result ofimpedance mismatches between the lead fingers and associated IC die orbetween the leads or traces and external circuitry, may distort normalsignals propagating concurrently with the reflection signals. And,magnetic fields created by signal currents propagating through the leador trace-associated inductance can induce currents in adjacent leads ortraces, causing crosstalk noise.

Therefore, the state of the art die and package configurations describedherein are having difficulties in keeping up with the trend towardsfaster devices at lower power. Noise problems are exacerbated by use ofa large number of laterally adjacent traces of substantial and varyinglengths extending from centralized die location to thehorizontally-spaced, offset locations of vias extending to solder ballsor other conductive elements for securing and electrically connectingthe package to a carrier substrate.

There are various constraints that limit the number of signal tracesthat can be fabricated on a package. Industry standards impose specificrequirements as to the spacing between solder balls, thereby restrictingthe spacing between the vias that electrically connect the signal tracesto the solder bumps. The spacing restriction limits the number of signaltraces that can fit between the vias which, in turn, limits the numberof signal traces that can be used to carry signals to and from the die.Current fabrication technology imposes minimum pitch requirements forsignal traces to attain satisfactory yields and to ensure mechanical andelectrical reliability. The limitation on the maximum number of usablesignal traces limits the maximum number of solder bumps, thereby placinga ceiling on the number of signals that a particular package canprovide.

There are several levels of interconnections that make up anencapsulated integrated circuit. First, there are the internalinterconnections of the circuit making up an individual die. Then thereis the interconnection between the various dies themselves, especiallyif more than one die is in a package. There is also a connection layerbetween the dies and the package that allows external access.

With respect to the package connection, wire bonds are typically used toelectrically connect the input/output (I/O) pads of the die to traces orpads on the package. If the die is on the side of the circuit boardinside the package opposite the solder bumps, conductive vias are formedthrough the circuit to conduct signals from the solder bumps to the padsor traces. To enable routing in highly dense integrated circuitpackages, there are many techniques known to those skilled in the artsuch as micro-vias, blind vias, buried vias, staggered vias.

A further problem with higher density and more complex circuit designrelates to the verification at all the various steps along the process.As the number of layers and the die size increase, the resources tovalidate the different steps including the design rules of the layoutsof the different layers increase exponentially.

In addition, the static power is greater due to leakage through the thinoxides required for the higher density circuits. There is also anincrease in the number of conduction and concomitant dielectric layerswhich must be traversed to reach various parts of a given die and tointeract with other dies. This increase gives rise to increased problemswith layer to layer registration, step coverage with its potentialfailure modes, contact integrity, and validation problems. Because ofaspect ratios, stepped vias must generally be used in most cases at thesmaller feature sizes. However, using the stepped vias adds anadditional mask layer for each such stepped via. Planarity also becomesmore difficult with the denser circuits.

As noted herein, the existing packaging fail to address several criteriarequired for high density, high speed and low power packaging, namely:interconnections with non-planar die resulting from many layers on thedie; limitations on the fanin/fanout; inability to monitor flip-chippackaging signals; and, very long signal travel paths resulting insignal reflection, degraded signal integrity, propagation delays,switching noise, crosstalk and dispersion. Therefore, what is needed isa mechanically and electrically desirable packaging scheme toaccommodate high density high speed, low power packaging. Such a systemshould interconnect die without having to travel excessive paths andallow in-situ monitoring of critical signals. Ideally the system shouldbe easily implemented without affecting the current and expectedfabrication methods and machinery.

SUMMARY OF THE INVENTION

Accordingly it is a general object of the present invention to provide anovel and useful system and associated methods that can solve the priorproblems described herein. The foregoing needs are satisfied by theinventions detailed herein that alleviate the aforementioneddifficulties.

One embodiment of the invention is a system for interconnecting at leasttwo die, comprising a first die having a plurality of first dieconducting layers and first die dielectric layers, wherein the first dieconducting layers and the first die dielectric layers are disposed upona first substrate. There is a second die having a plurality of seconddie conducting layers and second die dielectric layers, wherein thesecond die conducting layers and the second die dielectric layers aredisposed upon a second substrate. There is at least one interconnectstructure coupling at least one contact of the first die conductinglayers on a side of the first die to at least one contact of the seconddie conducting layers on a side of the second die. As used herein, theterm contact includes any interface such that it encompasses both directcoupling and indirect coupling. Direct coupling methods include but arenot limited to rod, ball, dual balls, bar, cylinder, bump, slug,conductive contact pads, terraces, fiber optic cable, and carbonnanotubes. Indirect coupling methods include wireless plus inductive andcapacitive. Wireless methods include microwave, millimeter wave, andphotonic. For example, a contact can be a conductive contact in oneembodiment but also can be the interface with an active element such asa photonic device.

The interconnect structure can vary in shape and size, and may beselected from at least one of the group consisting of: rod, ball, dualballs, bar, cylinder, bump, slug, and carbon nanotube. Each die can havemultiple sides and the interconnect structure is coupled to at least oneof the sides.

The die can also have features to facilitate mating of the interconnectstructures such as dogleg cuts, grooves, notches, enlarged contacts,conductive contact pads, stepped vias, and terraces.

The die may include at least one three state bus coupled to theinterconnect structure allowing controlled fanin/fanout. The die canalso be cut or tapered at an angle that may facilitate the coupling ofthe interconnects. For example, the first die can be cut at a firstangle and the second die can be cut at an opposite angle. The term cutas used herein refers to the various manners in which the die can beshaped and includes the mechanical schemes such as cuts by saws as wellas cuts by etching processes and cuts and/or ablation by lasers ofappropriate wavelengths and powers. In one embodiment, the first dieand/or the second die have an angled die edge, and the slug has acorresponding angled slug edge, wherein the die edge and the slug edgeare intended to facilitate mating.

Furthermore, at least one other die can be coupled to at least one sideof the first die and/or the second die. There can be any number of die,wherein each die has multiple sides, and wherein any of the sides of anyof the die can be coupled directly or indirectly to each other.

The system may further include active elements in each of the first andsecond die providing indirect coupling, wherein the indirect couplingcan be inductive coupling, capacitive coupling, and wirelesscommunications. As used herein, wireless coupling and wirelesscommunications, refers to all forms of communicating in the fields ofmillimeter wave communications, photonic communications and microwavecommunications.

Another embodiment of the invention is a method for coupling at leasttwo die, comprising forming a first die having a plurality of conductionlevels and a plurality of dielectric levels, forming a second die havinga plurality of conducting levels and a plurality of dielectric layers,interconnecting at least one of the conductive contact pads of at leastone of the conducting levels of at least one side of the first die withat least one of the conducting levels of the second die. Theinterconnecting enables signals originating in at least one of theconduction levels of the first die to be coupled to at least one of theconduction levels in the second die without having to traverse allintervening conduction and dielectric layers of the first die and thesecond die.

The method can also include interconnecting simultaneously to couple tomore than one other die, and further comprising processing three stateoperations.

In another embodiment, the interconnecting from one of the first dieconducting levels to at least one of the second die conducting levels isnon-planar. Non-planar indicates that a conducting level from one diecan go to any of the conducting level on another die and is not merely aplanar coupling mechanism.

The interconnecting can be indirect coupling such as inductive coupling,capacitive coupling, and wireless communications. In one embodiment thewireless communications is provided by an optical device on the die,wherein the optical device can be, for example, PIN devices, MSMdevices, Edge Emitting Lasers and Vertical Cavity Surface EmittingLasers.

Another embodiment of the invention is an interconnect system forcoupling between die, comprising a first die having a plurality ofconducting layers and dielectric layers and a second die having aplurality of conducting layers and dielectric layers. There is at leastone interconnect structure coupled on a first end to at least one of thefirst die conducting layers on a side of the first die, wherein theinterconnect structure is coupled on a second end to at least one of thesecond die conducting layers on a side of the second die, and whereinthe interconnect structure electrically couples the first die to thesecond die.

The features and advantages described herein are not all-inclusive and,in particular, many additional features and advantages will be apparentto one of ordinary skill in the art in view of the drawings,specification, and claims. Moreover, it should be noted that thelanguage used in the specification has been principally selected forreadability and instructional purposes, and not to limit the scope ofthe inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings,wherein like reference numerals designate like structural elements.

FIG. 1a is a perspective view of a plurality of die interconnected bycorresponding balls or rods or other structures according to oneembodiment of the invention.

FIG. 1b is a perspective view of a plurality of die interconnected bycorresponding balls or rods or other structures showing multiple fanoutsaccording to one embodiment of the invention.

FIG. 1c is a perspective view of a plurality of die interconnected bycorresponding balls or rods or other structures showing multiple fanoutswith the fanouts operating as part of a bus from which one or moresignals could simultaneously be selected according to one embodiment ofthe invention.

FIG. 1d a perspective view of a plurality of die interconnected bycorresponding balls or rods or other structures illustrating laterallocalizing the interconnects according to one embodiment of theinvention.

FIG. 2a is a perspective view of three die interconnected on the sidesby connection balls with slanted die walls to aid in ball placementaccording to one embodiment.

FIG. 2b is a side view that illustrates the die interconnection byconnection balls for angled dies and various ball sizes according to oneembodiment.

FIG. 3a depicts an embodiment of two die cut with a notch section toaccommodate a larger interconnects along with a smaller sizeinterconnects according to one embodiment.

FIG. 3b shows four die interconnected by interconnects of differentsizes using again dogleg or notched cutback recesses to accommodate thelarger interconnects and -couple multiple die and multiple layersaccording to one embodiment.

FIG. 4 is a side view of two die interconnected by different sizeinterconnects and a structure showing both conducting layers anddielectric layers according to one embodiment.

FIG. 5 shows a side view perspective ‘slice’ of a die with contact“flanges” created using stepped vias or other techniques according toone embodiment.

FIGS. 6a-e shows elements of mask layers to create the stepped viaflanges according to one embodiment.

FIG. 7 shows a three-dimensional perspective view of a die with variousstructures and one dogleg recess according to one embodiment.

FIGS. 8a-8b show an application of the presenting invention inconjunction with photonic device structures wherein vertical beamsemanate from VCSELs and horizontal beams emanate from EELs according toone embodiment of the invention.

FIG. 8c depicts an application of the presenting invention inconjunction with photonic devices, microwave, millimeter wave, plusballs, rods, bars, and other structures according to one embodiment ofthe invention.

FIG. 8d shows multiple stacked die containing photonic device elementsand microwave and/or millimeter wave devices according to one embodimentof the invention.

FIG. 8e shows an application of the present invention for fiber opticcable connections according to one embodiment of the invention.

FIG. 9a illustrates a multi-layered interconnect device termed a slugand the relationship to one die, configured in accordance with oneembodiment of the invention.

FIG. 9a illustrates a multi-layered interconnect device termed a slugprior to being coupled to die, configured in accordance with oneembodiment of the invention.

FIG. 9b illustrates the slug coupled between die and configured inaccordance with one embodiment of the invention.

FIG. 9c depicts a further embodiment of the slug allowing multiple layercoupling, configured in accordance with one embodiment of the invention.

FIG. 9d shows serpentine and non-serpentine inductive interconnects usedto couple various layers between die and configured in accordance withone embodiment of the invention.

FIG. 9e illustrates one embodiment for coupling the slug onto a dieusing interconnects, configured in accordance with one embodiment of theinvention.

FIG. 10a shows another type of slug interconnect configuration usingterraced coupling between the slug and die according to one embodimentof the invention which shows multiple fanin/fanout and how a givensignal on one die can connect to another die without having to traversemany layers on the two die.

FIG. 10b is a further illustration of the terraced coupling between theslug and die according to one embodiment of the invention.

FIG. 10c shows field or mask programmable slugs used to connect signalsfrom one die to another die.

FIG. 10d shows an active element slug (which could itself be anotherdie) interconnect configuration with terraced coupling between the slugand one die and non-contact coupling using photonic, microwave, and/ormillimeter wave devices to connect to other die according to oneembodiment of the invention.

FIG. 10e shows a cut-away perspective view of the various layers and thecontact pads coupling therein according to one embodiment of theinvention.

FIG. 11 is a top perspective view of a board having a substrate withmultiple die of various sizes and illustrates the sidewards interconnectaccording to one embodiment of the present invention.

DESCRIPTION

The methods and embodiments of die interconnections disclosed hereinenable improved circuit designs with better performance and ease ofmanufacturing. Please note that figures are only a few of the possibleembodiments and are presented to demonstrate features of the invention.The figures are not drawn to scale. In particular some parts aremarkedly misplaced or drawn larger or smaller than normal so as toemphasize certain points.

The term die is loosely used herein to refer to any substrate(s)including but not limited to dies in the usual sense but also, forexample, substrates containing so-called hybrid devices or even onlypassive devices. The term chip(s) is sometimes used interchangeably withthe term die. The term die may imply more than one such structure.Likewise, the use of the term “interconnect” refers to the couplingamong die and is not limited to any particular form of interconnectingstructure. Also, the term “signal” is used to designate any type ofcommunication among dies in the package. Some of the particular formsinclude digital, analog, microwave and millimeter wave, photonic,waveguide signals of various mode types and polarizations, as well as DCpower. The term signal may also include inductive and capacitivecoupling techniques.

In addition, terminology regarding conducting layer (CL) and dielectriclayer (DL) are used for convenience and there is no significance to thevariation in the pattern used to denote the conducting layers. Accordingto certain embodiments the lower layers of the die containing the activeand/or passive elements and the substrate are not shown, but these aretypically located at the bottom of the conducting layer “stack.”Moreover, the conducting layers are often shown as a slab like structureof conducting material for clarity of explanation. It is fullyrecognized that multiple fabrication methods are possible, includingvariations of the Damascene process. The manner of fabrication does notaffect the functionality of the present invention.

It is understood that a configuration in which multiple fanouts isdescribed could generally be reversed to permit multiple fanins. Unlessnoted otherwise in what follows the term interconnect or listing of anyone type refers to any of the many types of interconnects both direct,such as balls, rods, bars, cylinders, bumps, slugs, and carbonnanotubes, and indirect such as photonic, microwave, millimeter wave,capacitive, and inductive.

Referring to FIG. 1a , the top view perspective shows several die 10,15, 20, 25, 30 of varying shapes and sizes all coupled by a plurality ofinterconnect balls 40. The side connection structures 40 interconnectingthe die 10, 15, 20, 25, 30 avoid the planarity problem that exists withtrying to properly align solder balls to the surface of the high layercount dies, as well as to those with different thicknesses due todifferent layer counts and different starting wafer thicknesses.

In this embodiment, the interconnects 40 are a pair of connecting balls,wherein various side interconnects are detailed. Die 10, 15, 20, 25, 30can have numerous layers and differing heights across the surface of thedie 10, 15, 20, 25, 30 making solder ball connections On the topmostactive surface of the die difficult, whereas the side interconnect 40does not depend upon the planarity of the top of the die. Connecting onthe sides, and more particularly to conducting layers on the side, alsoeliminates the excessive travel length of a signal traversing throughthe many layers of the die.

The solder or other attachment interconnect 40 between the die 10, 15,20, 25, 30 is shown as two ball structures, wherein a ball would bedeposited on one die at a certain layer level and a corresponding ballwould be placed on the adjacent die at a certain layer, and wherein thetwo balls would be mated to each other thereby coupling the two die. Theterm ball is used to denote any object used for interconnect which hassome form of rounded or arcuate surfaces including a bump, and it may ormay not be elliptical in cross-section.

A number of types of interconnects are presented herein many of whichcan be used in combination, including balls, rods, bars, bumps, carbonnanotubes, and other similar structures provide direct coupling. Thus,single balls, multiple balls, rod like structure, bars, nanotubes andother similar structures, or some combination thereof are within thescope of the invention. Thus, although FIG. 1a shows balls 40 on eachdie 10, 15, 20, 25, 30 butting against balls 40 on adjacent die, afurther embodiment is an implementation in which only one ball is usedto connect the two adjacent die which may be preferable formanufacturability.

For illustrative purposes, certain dies for 125 and 150 millimeterwafers are typically 14 mils (thousandths of an inch) or about 350microns thick. Solder balls used for connections are currently only 40to 50 microns or approximately one-seventh ( 1/7) of the size of thewafer, however the size of the solder ball can vary depending upon theequipment used to deposit the balls. Ball sizes such as 5 microns orless are within the scope of the invention as the intent is to couplebetween adjacent die and improvements in the manufacturing technologywill allow very small interconnect sizes for the interconnect 40. Forfurther example, 200 and 300 millimeter wafers that are typically 625microns and 720 to 750 microns thick respectively, have active layersthat are 10 microns thick. These larger thicknesses mean there is moremargin with respect to implementing some of the features of thisinvention. Ultra-thin die represent a further embodiment.

It should be appreciated that the interconnect dimensions are smallerthan the 4 mil or 100 micron bonding pads currently used, and thus havecorrespondingly lower capacitance. Typically, most of the electricalactivity takes place within 20 to 30 microns of the surface of thewafer, although it varies widely and may be much deeper in manycircumstances. DRAMS for example use trench isolation that goes to adepth of greater than 10 microns. Some 300 mm wafers have conducting anddielectric layers that are 10 microns thick.

By way of further example, die with eight or more metalization layersplus two or more silicide conducting layers with concomitant nine toeleven dielectric layers plus twenty or more layers to form the actualtransistors can have active regions in the 300 microns region. Thus, thevertical dimensions of the present invention are well within the rangeof that which is commonly practiced.

FIG. 1b illustrates multiple fanout and busses that are driven andelectrically coupled according to one embodiment, wherein a signal 65 onone die 50 fans out to inputs 71, 72, 73, . . . 7 n on another die 55through an interconnect bar 60. As depicted, a signal 65 along aconducting line trace 66 on dielectric layer 52 of one die 50 iselectrically coupled to a contact pad 68 that is coupled to aninterconnect bar 60. The interconnect bar 60 is then electricallycoupled to at least one corresponding contact pad 78 associated with atleast one respective conducting line trace 76 that is associated withthe signals 71, 72, 73, 7 n on a dielectric layer 54 of another die 55.The signals 71 72, 73, 7 n could also go to other logic on-chip oroff-chip. By way of one example, if any of the signals 71, 72, 73, 7 nare inputs to a three-state bus, signal 65 is driving that bus. Theinterconnect bar 60 need not couple all of the signals 71, 72, 73, 7 nfrom one die 55 to a single signal 65 on another die 50, and in otherembodiments there may be more than one signal from one die that iscoupled to a section of interconnect bar and fans out to at least one ofthe signals on another die. Other variations employing a combination ofinterconnect bars and single interconnects such as balls and rods arealso within the scope of the invention.

The contact pad 68 as described herein is part of the broader contactsdescribed herein which includes not only conductive pads and enlargedcontact areas, but also includes active element contacts.

Another embodiment is illustrated in FIG. 1c in which input signal 65drives a three-state bus 80 which has controls 81, 82, 83 . . . 8 whichdetermine which of elements 70, 71, . . . 7 n write or read (eg: chargeor discharge) to/from the bus. The signal 65 is electrically coupled viaa trace 66 and contact pad 68 disposed on a dielectric layer of one die50. The interconnect bar 60 couples the signal 65 from the first die 50to the second die 55, wherein the three state bus 80 having the controls81, 82, 83, 8 n allows control as to the coupling of the input signal toone or more of the input signals 71, 72, 73, 7 n. The conducting traces76 are deployed on the dielectric layer 54 of the second die 55.

Referring to FIG. 1d , a further embodiment shows grooves 46 and notches44 in the die 25 to position balls 45, rods 41, and other interconnectstructures if necessary in one or more implementation. In thisparticular embodiment, the die 25 has grooves that facilitate the matingof the single balls 45 to electrically couple with another die 15. Thedie 25 also has notches 44 that facilitate the mating of the rods 41that couple to another die 26.

FIG. 2a is intended to illustrate some of the variants applicable to thepresent invention. Referring to FIG. 2a , a side perspective view isillustrated noting that the interconnects 230 couple between severaladjacent die 200, 210, 220. As shown, multiple adjacent die can beoperatively coupled to each other via the side interconnects 230 and theangles and positioning of the opposing and proximate die 200, 210, 220do not have to be equivalent. There can be any number of side or lateralinterconnects 230 that can couple a certain layer of one die to a layeron an adjacent die. The interconnection can couple layers that are atapproximately the same level, approximately parallel, or can couplelayers with some vertical difference depending upon the angles and sizesand types of the coupling structures. Furthermore, the use of slugs andnon-direct contact structures such as active element contacts aredetailed herein and allow other coupling options.

Referring again to FIG. 2a and FIG. 2b , the walls 240 of the die 255,260 are slanted to aid in the interconnect 230, 250 placement. In moreparticular detail, FIG. 2b shows a side view perspective of oneembodiment of the present invention for multi-layered die 250, 260. Inthis embodiment the multi-layered die 255, 260 have an angled or tapereddie edge 240 between the opposing and proximate die. There can bedifferent sized interconnects 250 as the spacing between the adjacentdie 255, 260 varies due to the angled walls 240. Other interconnectstructures 250 such as rods, bumps, bars, and carbon nanotubes can beused alone or in combination with the other interconnects employing theangled wall configuration especially if coupling among specific layersof the die having different vertical heights.

It should be readily apparent that one or all sidewalls 240 of each thedie 255, 260 can be tapered and the taper angle can be calculatedaccording to a desired spacing of the interconnects 250 for a particularlayer. In this particular embodiment with at least one of the adjacentdie having a tapered die edge or sidewall 240, the interconnects 250 canbe varied in size to accommodate the difference in the separationbetween the die 255, 260. While die traditionally have four sides, anypolygonic die benefit from the present interconnect invention.

This angled or tapered wall 240 can be fabricated by arranging the widthof adjacent stacked layers such that an upper layer can be slightlyoffset, thereby resulting in a tapered, terraced, or angled appearance.Alternatively, the die edge 240 can be cut using a wafer saw and/or alaser ablation “saw” depending in part on the materials used. It is alsowithin the scope of the invention to employ non-linearity to the taperedwall such that it can have varying shape and accommodate lateralnotches, steps or grooves (not shown).

Referring to FIG. 3a and FIG. 3b , a further embodiment for coupling dieis illustrated, visually demonstrating single or multiple fanin/fanoutcapabilities. FIG. 3a shows two die 330, 340 with a dogleg cut 320between the die. Small interconnects 300 couple the lower levels betweenthe die 330, 340. A large interconnect 310 couples the die within theregion of the dogleg cut 320. The dogleg cut 320 can be accomplished inmany ways as is known in the art, such as by using a wafer dicing saw,laser ablation, or masking techniques as described herein. The largeinterconnect 310 provides one mechanism for multiple fanin/fanout bycoupling layers to/from multiple die as shown in FIG. 3 b.

FIG. 3b shows four die 350, 355, 360, 365 interconnected by balls 370,375 of different sizes using again dogleg cutback recesses 320 toaccommodate the larger ball 370 and/or other structure sizes 375. Thetwo die on top 350, 355 have been flipped over. The interface area 380between the top die 350, 355 and the lower die 360, 365 can be coupledusing interconnects such as balls or other structures thereby showingtop and side coupling of die using interconnects. The interface area 380in one embodiment may also represent a heat conductor/spreader orinterposer.

Referring again to FIG. 3b , there are four die 350, 355, 360, 365 thatare coupled to each other via a plurality of large interconnects 370 andsmall interconnects 375. In addition, there is a heat conducting layer380 that provides a thermal transfer mechanism. While the smallinterconnects 375 can be used to couple between conducting layers ofproximate die, such as die A 350 and die B 355, the large interconnect370 allows for coupling to one or more conducting layers of more thantwo die in this case to all four die 350, 355, 360 and 365.

The heat conducting layer 380 which can also function as an interposercan be brought out to a cold plate or other cooling mechanism such asdie liquid cooling. Moreover similar to the multiple fanouts, barconnector could be used in conjunction with connectors 370 and 375 andthe shape could be, for example, spherical, cylindrical or rectangular.

The dog leg recess 320 not only allows larger connecting structures butalso provides a means to locally position the ball, rod, bar, and/orother structures in the vertical dimension. And, it is not restricted tomultiple fanouts.

Referring again to FIG. 3b inductive coupling is shown for both top andside. Embedded in the top and sides of dies 350, 355, and 365 areinductive couplers, namely Vertical inductive coupling elements 382 andHorizontal inductive coupling elements 384. There is a differencebetween the vertical and horizontal because the former may span morethan one conducting layer. The transposer/heat remover 380 might also beremoved where horizontal inductive elements 382 exist depending upon theamount of separation of the two die as well as other factors describedherein. A heat conductor/spreader or interposer is known in the art andsome embodiments further include conductive elastomers.

As is well-known, inductance slows the signal down and is oftendeleterious. However, inductance can be used for non-direct (also termedindirect contact) interconnect as shown below in FIG. 3b . It is commonin analog microwave and millimeter wave devices to build inductivecircuit elements on chips. Some of the design factors for the inductorsinclude the degree of coupling and the implementations depend uponseveral factors including the frequency, the permeabilities of thematerials being used, the proximity to each other, and the currentsflowing.

In addition to spiral inductors, common in microwave and millimeter waveapplications, it is also possible to use serpentine and interdigitatedstructures.

For field effect transistors the serpentine and interdigitatedstructures enable high width over length ratios, which is a measure ofdrive capability for a given feature size and technology, and providesthese favorable ratios in a small form factor. For a further descriptionof this for background purposes, see E. Hollis: “Design of VLSI GateArray ICs”, Prentice-Hall, 1988. However, similar structures can be usedto provide inductors albeit without, of course the sources and drainsused in the transistors. The serpentine structures according to oneembodiment herein correspond to the gates of the transistors. Thematerial used for the inductors would most likely be dissimilar fromthat used for the gates.

A cut-away side view perspective of a vertical slice of a first die 405and a second die 410 is shown in FIG. 4 showing a multi-layered dieaccording to one embodiment. A plurality of conducting layers 430 suchas metal, polysilicon, and silicide are interspersed with a plurality ofdielectric layers 420 and are vertically stacked to form each of the die405, 410. The materials and types of layers depend upon the designcriteria and fabrication techniques employed. There can be a number ofsmall interconnects 455 coupling any number of the conducting layers.Interconnect rods 440 can also be employed to couple adjacent conductinglayers 430 between the dies. Also shown in a dogleg cutout 415 with alarge interconnect 450 that is used for coupling to other die (notshown). The width of the layers 420, 430 can be varied to accommodatecertain design criteria. For example, the use of the large interconnect450 may require a thicker dielectric layer about the conducting layerthat interfaces with the large interconnect to ensure it does not coupleto other conducting layers in the same die. It should be readilyapparent that two die can be interconnected by different size balls andin combination with a rod or a bar is well within the scope of theinvention. The variety of configuration options may be useful formultiple fanouts and bus addressing.

FIG. 4 also illustrates both conducting layers and dielectric layersthat form the stack. With respect to the conducting layers, a variety ofmaterials are used for conduction, and qualities include conductivity,adhesion, impenetrability by other materials, well defined stop etchingparameters, step coverage difficulties, compatibility with existing orproposed processes, and manufacturability. For pure metal layers, copperwhich has a melting point of 1083 deg C. and refractory metals such astungsten, titanium, molybdenum, which have melting points around 2500deg C. are typically used. They are also used over polysilicon to formsilicides which have greater conductivity than the polysilicon alone.Because silicides are native to the self-aligned gate (SAG) process, twosuch layers are generally used to aid in conduction for relatively shortdistances. Variations of the Damascene process in which metal isdeposited into indentations in dielectric are often used. The termconducting material thus typically refers to various metals used in theprocess such as, but not limited to, Al, Cu, and refractory metals suchas molybdenum, titanium, tungsten, as well as polysilicon, silicides,and other materials having satisfactory properties. Increasingly carbonnanotubes are being used partly because of superior thermalconductivity. Tools to enable greater precision of manufacture areconstantly being developed and what may be limitations of the currentstate-of-the-art should not be used as a gauge to unnecessarily limitthe present invention. Nonetheless, a permutation of what is shown inprevious and other figures enable greater contact sizes to be used.

As shown in FIG. 5 the contacts to the die extend over greater than oneconducting layer as shown. The method of doing this is straight forwardand employs a variation of what are known as “stepped vias.”

The method detailed herein shows the creation of an enlarged taperedcontact pad, and a similar method can be used to create othernon-tapered contact pads. The method depends upon a number of factorsincluding but not limited to equipment types. In general, smallercontact pads are desired for several reasons, such as lower capacitanceand hence faster speeds as well as the ability to put more on a givendie of slug

The formation of a die in one embodiment of the invention is illustratedin FIG. 5 in which the subscripts denote the various mask layers. Inthis embodiment, the connections to the sides of the die are shownwherein a signal on a conducting layer is brought to the interconnect bylaying out that conducting layer mask appropriately. In this embodimentthe interconnections along the sides of the die are provided by creatingbonding pads via stepped vias. The bonding pad embodiment for the I/O isparticularly useful when the interconnect dimensions exceed theinterlayer spacing and it would difficult to place an interconnect onthe side and only interface with a single conducting layer.

Referring again to FIG. 5, a plurality of dielectric layers (DL) 540 andconducting layers (CL) 530 are vertically stacked on the base substrate510 in the formation of the die 505. Because the focus of this inventionis on interconnect, the term “substrate” is loosely used to include theactive element layers not shown in the Figures.

The stepped vias according to this embodiment is formed from two or moresuccessive dielectric masks and having stepped via conducting portions560 and stepped via dielectric portions 550. The datum lines 551, 552and the edge of die 553 show the reference planes in relation to the die505. As depicted, there are a number of conducting layers 530 commencingwith CL_(N) 513 formed on the base substrate 510 followed by adielectric layer DL_(N); conductive layer CL_(N+1); then dielectriclayer DL_(N+1); wherein the processing continues until the upperdielectric layer.

Stepped vias are a standard masking technique and are normally employedto mitigate the effects of poor “step coverage” due to poor aspectratios when connecting among layers. As known in the art, a stepped viais a vertical opening which can be filled generally but not always withconducting material which is larger on one or both ends than in themiddle. Typically they are used to prevent the deadly “step coverage”problems in going from one conducting layer to another conducting layer.In one method, a dielectric layer which is not of full thickness is laiddown and patterned with a hole of the size of the via desired. A seconddielectric layer of thickness which when added to that of the previouspartial layer gives the overall dielectric layer thickness desired isthen put down. The via opening in the second partial dielectric layer islarger than that of the first partial dielectric layer and helps avoidthe step coverage problem.

In this invention, techniques somewhat similar to those employed in thevertical stepped vias are used to create a “flange” contact from tracesrunning to the side edge of the die. The flange is an enlarged contactarea to enable more margin in interconnect using side interconnects.

It should be readily understood that while only one trace going to aside bonding contact is shown in FIG. 5 and FIG. 6, more than one suchtrace could be made to the same contact from either the same ordifferent conducting layers encompassed by the flange. This systemprovides yet another method for multiple fanin/fanouts.

One of the benefits of a stepped via is that the opening on one side ofthe connection is made larger than on the opposite side of theconnection by simply having more than one mask for the via as iscommonly done for vertical stepped vias. The stepped via thus provides alarger side area of the die for coupling to an interconnect.Furthermore, it can also establish a ‘seat’ for the interconnect, suchas a rod, bar, bump, ball or other interconnect. As noted herein, any ofthe designs involving balls, rods, and/or other structures, may include“troughs” cut about the die to localize the placement of the structures.

Referring again to FIG. 5, the area between the reference planes for thedatum line 552 and the edge of the die 553 includes areas of expandedheight stepped via dielectric portion 550 and expanded height steppedvia conducting portion 560 wherein the conducting portion 560 forms theover-sized contact 554.

As noted herein, while it is convenient conceptually to describeconducting layers, all conductors whether contacts or lines are enclosedin dielectric material except when they join with other conductors. Thusthe dielectric layers actually extend into the conducting layers such asnoted by the Damascene process, or are deposited by the next successivedielectric layer around the conductors etched from the conducting layer.

The formation of the stepped via of FIG. 5 according to one embodimentis shown in more particular detail in FIGS. 6a-6c which illustrates atop view perspective of a vertical slice showing how contact 554 onconducting layer CL_(N+1) 515 is enlarged to give more margin inplacement of the mating edge contacts. Note that just one enlargedcontact pad is created from the process below. Even though it overlapsin this case two additional conducting layers above it, and if desiredone or two below it, the enlargement could encompass just one suchconducting layer either below or above it. Thus there is a large amountof flexibility to accommodate a wide variety of needs and precisions ofequipment types.

FIG. 6a thus shows in effect 2 successive layers, DLn and CLn+1. FIG. 6bshows only one layer, DLn+1 which is the next higher dielectric layer.FIG. 6c is similar to FIG. 6a in that it shows 2 layers, DLn+1 andCLn+2.

FIGS. 6a-6c show the formation of the stepped via in FIG. 5 but from atop perspective. The mask layers, as noted in FIG. 5, are verticallystacked conducting and dielectric layers that provide for the formationof stepped or non-stepped vias and the corresponding coupling via theinterconnects (not shown). To avoid excessive repetition, only a portionof the enlarged contact 554 is shown.

In this example, referring to FIG. 5, the enlarged contact pad 554 ismade to extend “upwards” to encompass two more conducting layers 517 and519. It is isolated from other conducting layers by the dielectriclayers 518 and 520. In each case, the conducting material from the nexthigher layer fills the hole in the dielectric purposely created for suchfilling by the respective mask for that layer.

Referring to FIG. 5 and FIG. 6a , trace 653 provides the inputs/outputto/from the contact pad 654 is formed with conductive layer CL_(N+1)515. The trace 653 is shown surrounded by dielectric layer DL_(N) 514employing the Damascene process. If an older process is used, the trace653 would be surrounded by the next higher dielectric layer 516 (notshown). The following is a description of one embodiment using theDamascene process. It will be readily apparent to those skilled in theart how the older processes can also be used.

Referring to FIG. 5 and FIG. 6b the contact pad layer 654 is processedwith dielectric layer DL_(N+1) 516 and further processing as is known inthe art forms an opening 660. The opening 660 is provided in order forthe conductive material such as metal to be deposited from the nextsuccessive upper conducting layer 517 CL_(N+2). FIG. 6b shows theopening in DL_(N+1) which will be filled by the next conducting layerCL_(N+2) 517. For clarity in presentation, two different patterns areused for the DL_(N+1) 516 material even though they are the samematerial. One embodiment provides for a portion of the larger opening indielectric layer DL_(N) to be closed off to provide part of the taper tothe flange.

In FIG. 5 and FIG. 6c the deposition process is shown repeated for theupper edge of the pad 554 to make all the desired contacts and steppedvias. In each case the next conducting layer fills the hole in thepreceding dielectric layer. Because of the high temperatures used insubsequent processing, copper and/or refractory metals may be used. FIG.6e also shows that the void in dielectric layer DL_(N+1) 516 has beenfilled with material from conducting layer CL_(N+2) 517 to extend theflange into the CL_(N+2) layer 517.

FIG. 6d and FIG. 6e show a second iteration of the above process stepsdepicted in FIG. 6b and FIG. 6c to further taper the contact flangeaccording to one embodiment of the invention. FIG. 6e shows the void inDL_(N+2) which has been filled with conductive material from 519CL_(N+3) and surrounded by dielectric, material from 520 DL_(N+3).

Referring to FIG. 6d , the processing continues having the opening 662partially filled with dielectric material from the DL_(N+2) layer 518.In FIG. 5 and FIG. 6e , the top of the flange is shown filled withconductive material CL_(N+3) material 519. Similar masking steps areused to create other conducting pads/contacts. For example, to createthe dogleg in the tops of dies 405 and 505, the masks would simply beappropriately dimensioned to shift the reference planes back. Furtherexamples are described herein. It should be readily understood that theterm contact includes not only the enlarged conductive contact shown inFIG. 6a-6e , but also includes the active element contact that may beprocessed in the die and provide for side edge communications.

Another embodiment of the present invention is illustrated in FIG. 7. Aspreviously described, a die 700 is formed from a vertical stack oflayers of dielectric layers 730 and conducting layers 740. On the sideof the die 700 there are a plurality of pads 750 and interconnects 710,720. This embodiment shows both the interconnect balls 710 as well asrods 720 on the same surface. The pads are brought out from therespective conducting layer and the pads 750 can be positioned anywhereabout the side of the die as shown and typically will be positioned withsome separation from other pads 750. There can be more pads 750 thanactual couplings to the balls 710 or rods 720, allowing for designflexibility. There can also be multiple pads 750 and interconnects 710,720 coupled to a single conducting layer in order to allow multiplefanin/fanout. The pads 750 and the interconnects 710, 720 can bedifferent sizes and shapes. The stepped via 760 is shown such that theside edge of the die for the stepped via portion is shifted in thehorizontal plane.

The present invention has numerous applications and some are providedherein by way of illustration of a few of the possibilities. Forexample, one application relates to interconnecting photonic chips, suchas Edge Emitting Lasers (EELs) and Vertical Cavity Surface EmittingLasers (VCSELs) to indicate the type of arrangement and communicationpossibilities but is not to be construed as limiting.

Referring to FIG. 8a , there are three chips 800, 810, 820 proximate thesubstrate 830. A photonic emitter 805, such as an Edge Emitting Lasers(EEL), is embedded in at least one of the sides of the chip 800 andradiates signals 840 to a photodetector in another chip 810. Thephotodetector on the other chip 810 may be any of several types such asPIN photodetectors which are small and which have excellent D* ratings,which is a measure of detectivity. Edge Emitting Lasers can alsofunction as photodetectors although they are not as good as PIN types.

In this example chip 810 contains another type of photonic emitter suchas a Vertical Cavity Surface Emitting Laser (VCSEL). Unlike the EdgeEmitting Lasers which radiate out the side, VCSELs radiate out the topof the chip. FIGS. 8a-8d are intended to show some of the optionsobtained by using side and top photonic devices, although each can beused independently.

In FIG. 8a , the photonic emitter such as a VCSEL radiates to aphotodetector in die 820 and also to the top cover of the package. Thereflection due to the latter would then spread the relatively narrowphotonic beams into roughly omni-directional signals which could then beused to connect with non-adjacent die, if desired. Multiple beamphotonic devices such as VCSELs are well-known.

Edge Emitting Lasers, VCSELs, and PIN photodetectors are very small. Forexample, the Edge Emitting Lasers are roughly the size of a conventionalbonding pad, enabling hundreds of them to be used in a chip, if desired.

The small size also enables “active element packages.” These arepackages which contain communication devices. For example,photodetectors receive the signals from an Edge Emitting Lasers and/orVCSELs without the need for bonding wires. These signals are in turn beused for in-situ monitoring of signals as well as for communicationdirectly to a printed circuit board (PCB) or other structure.

Referring now to FIG. 8a , as noted there is also a photonic transmittersuch as a VCSEL on the second chip 810 that radiates one or more signals850 to photonic detectors on another chip 820 and possibly also to aanother device or to a cover (not shown) which will then turn thesignals or beams into a semi-isotropic beam for transmittal to otherchips within the package. Note that the inputs for the photonic devicescould come from a rod, ball or other contact member as detailed herein.

FIG. 8b shows a bus made up of photonic transmitter or transceivers 805radiating signals 840 from the side of die 800 wherein the presentinvention permits the sideways communication ability between chips. Thesignals 840 can be unidirectional or bidirectional. The photonicscommunications can be implemented in numerous ways, such as digitalspread spectrum, wavelength division multiplexing (WDM), or othertechniques to enable simultaneous operation. According to thisembodiment, the width of the photonic emitter device can be about 4 mils(100 microns), and there could be at least 75 or more on each edge of a600 mil square die permitting the chip to communicate in four sidewaysdirections in addition to transmission/reception from the bottom and topsurface, thereby having a chip with communications in six planes ofpotential communication capability.

Referring to FIG. 8c multiple chips or dies 860, 862, 864, 866, 868 areshown having different shapes and of different thicknesses, which may bein part due to differences in numbers of layers and starting waferthicknesses. In this depicted embodiment, a microwave or millimetersource in Chip B 862 radiates signals 863 to dies 866 and 868 with itsrelatively broad beam whose beamwidth depends on the combination offrequency, aperture size, and antenna type. Between Chip A 860 and ChipC 864 are interconnects on one of the sides of each having interconnects870 and 872 coupling the chips. Coming out another side of die 860 areone or more Edge Emitting Laser or other photonic signals 861 whosebeamwidth encompasses both die 868 and 866. Although the photonictransmitter or transceiver is shown on die 860 it could be on any one ofthe dies.

FIG. 8d shows multiple chips 880, 881, 882, 883, 884, 885, 886, 887deployed about a substrate 830 and communicatively coupled to eachother.

In this embodiment, one of more beams or signals 892 are derived from aphotonic transmitter or transceiver 890 and transmitted to one or moreof the chips. There can be one or more photonic detectors 882 on atleast one of the chips that can intercept a portion of the beam 892 andextract the information therein. It should be noted that interposershave been omitted in the interest of clarity. As shown in thisembodiment, there can be hole(s) through the chips or the chips can betransparent or translucent to the wavelength of the photonic signal 892and a photonic detector or transceiver 891 can be located on one of theupper surfaces of the chip 880 to allow vertical transmission of data.While only one such photonic transmitter and one photonic detector aredepicted, there may be many such photonic devices such as VCSELs andEdge Emitting Lasers integrated into the chips. Note that putting holesall the way through the die to enable beam transmission is a routineoperation for many die types.

There are also interconnects 894 on the side of the chip that can beused in a contact or non-contact form and coupled to one or more of theother chips. These elements support the side edge communicationscapability as detailed herein.

The chips 880, 881, 882, 883, 884, 885, 886, 887 may be die of differentshapes, sizes and thicknesses and arranged in two or more separatestacks. One embodiment illustrating some of the communications includeshaving the Edge Emitting Lasers 890, 892 in die 883, 881 respectively,and communicating with chips 887, 885 and 884. As noted, the verticalbeamwidth of the Edge Emitting Lasers 892 typically communicates withmore than one chip vertically. However, the horizontal beamwidth whichis much smaller can be limited by using Edge Emitting Lasers whosehorizontal aperture size is large enough that only one die or evenpossibly part of one die is illuminated by the narrow beam. Thus, thepresent invention allows for one or more chips to communicate withoutdirect contact with one or more other chips of varying heights, widths,depths and aspect ratios on the substrate or suspended above it as inthe case of e.g., stacked die. This further includes communicating frommultiple sides of the chips and can further include communications tooff-chip resources.

Other side chip edge elements such as Edge Emitting Lasers 890, 892 canbe used in other embodiments to communicate data and information. Suchcommunications may be tunable and/or of a different wavelength dependingupon the application or they may use a coding scheme such as digitalspread spectrum.

Yet a further photonic connector of the present invention is to growfiber optic cables 897 to provide for chip-to-chip communications asshown in FIG. 8e . In this embodiment, the fiber optic cable 897 isgrown to couple die 896 with die 898. The growing of the fiber opticcable is established using the fabrication technologies as is known inthe art.

A further embodiment of the present invention introduces “slugs” as afurther interconnect embodiment. While the side mounted rods, balls, andother structures are useful for interconnecting die, another system toeffect the interconnect is to use slugs. The slugs are inserts betweenthe die to be interconnected, which in certain circumstances maysimplify and make the interconnects more manufacturable. The slugs alsomay act as interposers, analogous to the way the horizontal interposersare used in the current BGA methods of interconnect, to act as aninterface between elements of different thermal expansion coefficients.Thus the slugs represent a different embodiment for interconnection ofdie.

Slugs come in a variety of shapes and sizes and can be implemented in anumber of different manners. In one embodiment the shapes enable theside of the ‘client die’, the die interface to and which may house theslug, to be cut flush by the wafer cutter such as a saw or laser whichis used to ablate the die and/or separate the die from the wafer. Otherembodiments include angled cuts and terraced interfaces. Slugs may havecertain properties depending upon their purpose, design, usage, andfabrication. For example, one of the embodiments includes the use ofactive and/or passive components, such as inductors, capacitors, andcoils, used to facilitate non-contact or indirect contact. Otherembodiments include direct interconnect contact.

Furthermore, the slugs also permit connection to client die, multipledie, and also to another slug. The slugs can also include vias andinterconnects within the slug, which aid in translating as well asconnecting between client die and/or another slug. In addition, theslugs can have dimensions which traverse the entire side of one of itsclient die if desired. In one embodiment (not shown), one face of agiven slug may extend across all or parts of two or more client die.

The slugs can also have conducting and/or dielectric layers whichoverlap such layers above and below the initiating layer. For example,the layers and/or contacts on the slug can be thicker than the layer inthe client die or in the slug itself, just as the contacts can be in theclient die.

In some implementations the conducting layers can overlap verticallyand/or horizontally with similar structures on the client die. A furtherfeature of slugs is that they can be integrated into manufacturing usingtraditional machinery such as a ‘Pick and Place’ machine. And, the slugscan include interposer characteristics that can match different thermalexpansion coefficients.

Referring to FIG. 9a , a slug 910 is shown suspended above die A 900 anddie B 905 before final placement. The portions of the slug 910 which arebelow the conducting layers could be connected to the client die whichare connected to the substrate. The shape of the slug 910 is depicted ashaving a wedge shape however other shapes are within the scope of theinvention such as square, rectangular, terraced, circular and polygonic.Furthermore, for indirect coupling, the slug 910 does not have to beshaped to mate to the die and can be any shape that satisfies thefunctional coupling characteristics.

FIG. 9a is a vertical slice encompassing one or more conductive contactpads on each of the die and slug elements shown. According to oneembodiment the slug 910 does not have to connect directly to thesubstrate (not shown) although it may be desirable in some situationsespecially when the slug 910 contains active elements. The indirectcoupling between the slug 910 and the die 900, 905 can be an indirectinterconnect coupling using photonic, microwave, and millimeter wavedevices, and various combinations thereof. Inductive and capacitivecoupling are other indirect coupling possibilities and are well known tothose skilled in the art.

Depending upon the design of the slug 910, it can be used to couple anyconducting layer(s) of one die 900 to any conducting layer(s) of theother die 905. Furthermore, the slug 910 can include features allowingbus and fanin/fanout capabilities as detailed herein.

FIG. 9b shows the slug 910 directly coupled to the die 900, 905 and withthe conducting layers CL1, CL2, CL_(N) and CL_(N+1) of the two die 900,905 directly connected via the slug 910. In this embodiment, aconnection on conducting layer CL1 on die A 900 to CL1 of die B 905 viathe ball 918 on each side of the slug 916 does not have to pass all theway up through all the layers of die A and then down through all thelayers of die B 916. For example, there may be more than eighteenintervening conducting layers and dielectric layers to get to aconnecting structure on the top of the die A 900 and then go back downthrough the conducting layers and dielectric layers to get to conductinglayer CL1 on the other die A 900. The slug 910 does not have to have allthe layers of the die and can just employ a subset of the layersaccording to the desired requirements. Thus, the thicknesses of theconducting layers and dielectric layers of the slug 910 do not have tomatch that of the die A 900 and die B 905. The coupling via the ball 918is just one example of the type of interconnect structures that can beused to provide the direct coupling between the die 900, 905 and theslug 910. Instead of the ball, a bump or other members of the directconnection family described earlier could be used. Connection of die andslug without any intervening structure is also possible.

In certain applications, the larger the angle with respect to thevertical of the slope of both the slug and the client die, the moremargin there is in vertical placement and also in the placement of theslug and die themselves by, for example, a pick and place machine.Similarly, the margin for lateral placement can be increased byincreasing the lateral dimension of the contacts.

FIG. 9c shows how the vertical contact size of conducting layer CL2 inthat lateral spot can be enlarged for more margin via the contact flange922 and to permit easier connection. The lateral size of the contactflange 922 will depend upon many factors. Dielectric layer material 924surrounds the added ‘flange’ 922 on the contact to provide isolation forthe contact flange 922. In this embodiment, the contact flanges 922 onCL2 on die 920 are coupled to the conducting layers CL1 and CL3 aboveand below CL2 using the contact flange 922 and further coupled to acontact flange on slug 930, and then to a contact flange on die 925.Over and above simplifying the mechanical connection process, the flangealso enables busses, multiple fanouts, and other techniques as describedelsewhere.

The contact flange on the die A 920 may fanout to multiple contacts orto a bus on the conducting layer CL1, CL2, CL3 on slug 930 and die B 925if the latter does not have flanged contacts in that particular verticalslice. Note also that the fanin/fanout can, take place in twodimensions, both laterally with a wider contact on die 920, thus givinga wide range of possibilities. Furthermore, the slug 930 can havetransverse or diagonal conducting lines in order to couple a conductingline on one die that is at a different height on another die.

FIG. 9d shows a serpentine inductor 950 which spans four conductinglayers CL_(N−2) to CL_(N+1) and another inductor 955 which residessolely on conducting layer CL_(N). These could apply to the slanted dieand slug surfaces as well as to vertical surfaces such as shown in FIG.3b and FIG. 3c . Serpentine inductors, spiral inductors andinterdigitated structures are well known and described in detail in E.E. Hollis; “Design of VLSI Gate Array ICs”, incorporated by referenceherein and all within the scope of the invention. The serpentine andinterdigitated structures provide high width over length which is ameasure of drive capability for a given feature size and technology.However, similar structures can be used to provide inductors without, ofcourse the sources and drains used in the transistors.

The serpentine and interdigitated inductors have ultra-small dimensionsto couple the layers in the die to couple. Some of the benefits includebeing able to fanin/fanout to more than one layer if desired by thesimple expedient of connecting or not connecting traces to/from a givenlayer. The serpentine and interdigitated inductors achieve a largeamount of coupling area in a small form factor as opposed to running itall around the die layers. A further benefit of these inductors includesbeing able to get bidirectional elements by simply having traces on agiven layer or on different layers again to connect to one or more partsof the different “legs” of the serpentine.

FIG. 9e shows one embodiment for coupling the die 970 to the slug 975.In this embodiment, contact pad bumps 980 on the side edge of the die970 are coupled to conducting layers CL1 to CL_(N+1), which will then becoupled to slug 975. The bumps 980 could also be tapered rods or otherstructures that facilitate mating. According to one embodiment the slugcan sit directly on the respective die, such as on contact pads, therebyallowing a bare metal to bare metal coupling. The bumps 980 can beformed in a variety of ways including masking as detailed herein. Thebumps 980 could also be potentially grown in a manner similar to theliquid cooling pipes are grown or similar to the way in which carbonnanotubes are grown as contacts on the tops of dies. They could also beattached to an interposer or similar thermal spreader and then placed onthe side of the die. Depending upon the relative thermal characteristicsof the slugs and client die, interposers between slugs and die may ormay not be needed. Instead of using interposers between slug and die, itmay be preferable to use create metal or carbon nanotube heat pipes orsolid rods using vias to route the heat vertically to cold plates on thetops or bottoms of slugs or the die themselves. Heat pipes on the tophave already been developed elsewhere.

The formation of the various recessed layers or terraces is yet anotherfeature of the present invention. With this type of slug interconnect,the margin for horizontal placement can be increased by increasing thedepth of the terraces. Note that the thin contacts can be supported andstrengthened by adjacent dielectric. The recessed conducting layers anddielectric layers of the slug may be less deep than those of the die toprevent the conducting layers from shorting on the conducting layers ofan adjacent layer. The ends of the conducting layers may also be spacedwith dielectric for the same reason. Any of the previously describedelements including but not limited to balls, bumps, rods, bars or carbonnanotubes may be placed on any of the contact pads if needed or desired.

As noted, there are a number of methods for forming the recesses toachieve the terracing. Some of the methods include laser ablation,partial laser singulation, as well as in both mechanical and laserscribing used singularly or in combination. Laser ablation is onetechnique that occurs when the photonic energy corresponding to thespecific wavelength of the laser being used is greater than the bandgapof the materials upon which the laser beam falls. The photonic energy isthen absorbed by the material. A number of factors and tradeoffs existincluding a very wide variety of lasers and semiconductor materials.

Referring to FIG. 10a , one embodiment for a three dimensionalperspective view of a portion of a terraced die 1000 is shown,illustrating the conducting layers (CL), dielectric layers (DL) andcontact points 1010. The substrate 1005 may include a number of otherlayers as well, as the present invention can be integrated with existingfabrication processes and include any number of layers with or withoutthe sidewards interconnecting described herein. The various dielectriclayers and conducting layers are stacked to form the die 1000, whereinthe upper layers have a smaller width thereby creating the terracingeffect and providing a greater contact layer on the side edge. The datumline for CL_(N) 1020 and the next respective datum line for CL_(N+1)show the approximate width of the “step” 1026 or width of the extendedportion. The “riser” portion 1028 of the terracing is determined by thevertical height of the corresponding conducting and the dielectriclayers which, for example, may be 10 microns to 20 microns for 300millimeter wafers.

In this particular embodiment, the terraced edges of a respective pairof conducting layer and dielectric layer are approximately equivalentand in combination form the riser portion 1026. However, there is norequirement that the conducting layers and dielectric layers be pairedtogether. There is also no requirement that the conducting layers anddielectric layers be the same or similar thickness.

Conducting layer CL1 has been brought out in an exploded view to showthe interior view depicting one contact pad 1010 along with its trace1015 going to/from that pad. It should be readily appreciated that alarge number of such contact pads 1010 of different sizes can exist oneach side of each of the many conducting layers. It should also beappreciated that other connecting structures, such as but not limited toballs, bars, and rods can be used in combination with the terracedlayers.

As noted in the exploded view of FIG. 10a , the trace 1015 from contact1010 goes into the conducting layer CL1. It should be readily apparentthat it will go to other traces and other circuit elements. As in otherfigures only the salient parts are shown herein in order to illustratecertain features of the present invention. The mating surfaces on theslug or die may be the same size for fanin/fanout of one or of differentsizes for multiple fanin/fanouts and for busses or other uses.

Those skilled in the art will readily appreciate that the terracing ofthe die and the fabrication of the slug can be accomplished in manydifferent manners. According to one embodiment, the conducting layersare layers of metal, such as aluminum, copper, and/or refractory metals.According to one embodiment, the processing puts down a layer of metaland then etches it away. In another embodiment, using the presenttechnology implementing submicron feature sizes, variants of a‘Damascene’ process can be utilized wherein a dielectric layer is etchedaway and filled with metal(s). The manner of fabrication does not affectthe functionality of the invention.

The slug typically need not have all of the conducting layers anddielectric layers of the die with which it is coupled and can bedesigned to have only those conducting layers according to designcriteria. According to one embodiment, the mating contact pads on theslug are just the inverse of those on the client die. Other variationsinclude the use of multiple fanin/fanouts or bus connections. Variouspermutations are within the scope of the present invention.

As noted herein, one of the disadvantages with the present state of theart using BGAs is the lack of adequate fanout and/or fanin capabilitygreater than one. Similar disadvantages are present with respect todriving and being driven to/from busses of various types. A variety oftechniques are described herein using rods, balls, and other structuresin addition to integrating photonic and microwave/millimeter wavedevices that permit fanouts/fanins greater than one and for dealing withbusses. Slugs also can be designed with multiple fanin and/or fanoutcapabilities as well as multiple bus couplings.

According to one embodiment of the present invention, the lateraldimension of the exposed conducting layers of the die and slugs issignificantly larger than the access to such layers in the state of theart. For example, typical current die sizes are in the 500 to 600 milrange or greater. A very large contact to a single fanin/fanout wouldtake up less than 2 mils. Thus, a spacing of the fanin/fanout equal tothat single contact size means that a fanin/fanout of approximately 250to 300 can be attained, wherein typical fanin/fanouts are less than 10.This example is only intended to show that a very large number offanin/fanout device contacts can be placed on a single conducting layerand is not intended as prescribing any range or limitation. For example,large fanins are used in CPLDs and also in CPUs which use VLIW (VeryLong Instruction Words) of 128 bit busses.

In certain embodiments, the recessed conducting layers and dielectriclayers of the slug may be less deep than those of the die to prevent theconducting layers from shorting or otherwise interfering with theconducting layers of adjacent layers. The ends of the conducting layersmay also be spaced with dielectric portions.

Referring to FIG. 10b shows a vertical slice of layers of slug 1040making contact with the opposing contacts on a similar vertical slice indie 1030 and coupling to die 1035. There are a variety of ways to effectthe connection of the slug 1040 with its client dies 1030, 1035. Onecommon system for a ‘pick and place’ machine is to place both dies 1030and 1035 and then place slug 1040 to mate with them. According to oneembodiment a conducting layer on one die 1030 can be routed through theslug 1040 and couple to some other conducting layer on another die 1035.While the layers are shown to be approximately planar, there is notrequirement that the die conducting layers be about the same horizontalplane as the slug can shift the elevation and transfer to another heighton the other die. This is in addition to the various fanin/fanoutcapabilities described herein.

In a further embodiment, a signal 1050 on conducting layer CL1 of die1030 traverses through slug 1040 to signal 1055 on the conducting layerCL1 on die 1035. It should be noted that the signal path to get from die1030 to die 1035 using slug 1040 is much shorter than if the signal hadhad to traverse all the way to the top of die 1030 and then through thevarious layers of the other die 1035 all the way back down that to getto conducting layer CL1 on die 1035.

In yet a further embodiment, showing one example of fanning out insideslug 1040, the signal 1050 from die 1030 is routed not only as signal1055 via the conducting layer CL1 of die 1035 but also as signal 1060via a path inside the slug and to conducting layer CL3.

It is also within the scope of the invention to include certain signalprocessing or conditioning functions within the slug in addition to thesignal routing functions. Yet a further embodiment is the use ofprogrammable interconnects which could be either mask programmable orfield programmable to connect signals.

FIG. 10c is similar to FIG. 10b except that Application Specific Slug(ASIS) 1021 has programmable interconnects 1022 and 1023 which could beeither mask or field programmable to connect signal 1001 to signals 1013and/or 1014 as well as to 1017.

FIG. 10d shows yet a further variation of the slug providing a couplingbetween die using an active element slug which has one or more activeelements built into it. In this embodiment, a signal 1082 on theconducting layer CL1 on a first die 1070 is coupled to a transmitterdevice 1086 that transmits a signal 1084 to a detector element 1087 onconducting layer CL1 of another die 1075. The transmitter device can be,for example, various types of photonic transmitters and transceiverssuch as an Edge Emitting Laser, while the detector 1087 can be anintegrated photodetector such as a PIN device. The transmitter 1086 cantransmit a signal 1084 to any of the conducting layers or multipleconducting layers on the other die 1075. Furthermore, it is within thescope of the present invention that the transmitter 1086 broadcasts thesignal 1084 perhaps but not limited to digital spread spectrum signalsto the detector 1087. If the signal being broadcast is a digital spreadspectrum or similar, then multiple signals from multiple transmitterscan exist simultaneously, and is within the scope of the invention.Microwave or millimeter wave transmitters could also be on the activeelement slug with corresponding detectors on die 1075. Again, thecorrelation gain of direct sequence digital spread spectrum and similartechniques may be employed.

FIG. 10e is a simplified version of one of several masks that would beused in one embodiment to fabricate the terraces. Those skilled in theart will recognize the contacts 1083 and 1084 embedded in variousdielectric layers as discussed herein. Note that none of the masksrequired to form the terraces is unique or special to forming theterraces. Standard techniques and standardized equipment can be used.

An active element slug does not have to have its active elements on thebottom. This configuration will simplify and minimize the interconnectsin many cases. This configuration is in effect a die turned upside down.

One of the embodiments provides the ability to interconnect die ofdifferent thicknesses to enable technologies which are optimum for agiven function to be used, mixed, and interconnected in the samepackage. For example, HBTs are generally the technology of choice forA/D converters, low phase noise amplifiers, and photonic elements suchas Edge Emitting Lasers. On the other hand Si CMOS is generally thetechnology and structure of choice for most other applications becauseof low cost.

The dies may be of different thicknesses due to differences in numbersof layers and starting wafer thicknesses as well as different shapes.The present invention thus allows for a source, such as a photonic,microwave or millimeter source, in one die to radiate to one or morelayers in one or more die with a relatively broad beam. The beamwidthtypically depends on the combination of frequency, aperture size, andantenna type. Note that photonic, microwave, and millimeter signals canall be present simultaneously because of the very different wavelengths.Moreover, using techniques such as digital spread spectrum, differentcodes, different frequencies, and multiple sources of each type can bepresent simultaneously.

Referring to FIG. 11, one embodiment illustrating multiple chipsdeployed on a substrate is shown for illustrative purposes. A socketframe 1150 is coupled to a substrate 1100, wherein a center portion 1105of the substrate has some upward die 1120 coupled to the substrate withinterconnects on the top surface of the upward die for coupling todownward facing die 1125. The sizes and shapes of the die can vary andmultiple die couplings are shown. The downward die can couple directlyto the socket frame 1150 or to the contacts on the upward die 1120. Alsoincluded is a sideward die 1170 that couples to one of the downward die1125 via certain interconnects 1160. In this embodiment, the sidewarddie 1170 can couple to the downward die 1125 and may also couple to thesocket or an upward die 1120. While this particular embodiment shows adie to die coupling via an interconnect 1160 such as a rod or ball, theuse of slugs is also within the scope of the invention.

For illustrative purposes, suppose that for a given die there are 500 to600 Edge Emitting Lasers located on all four sides of the die andoperating on different wavelengths and/or using different digital spreadspectrum or other coding to prevent interference with each other.Alternatively one or more Edge Emitting Lasers could be addressing anumber of photodetectors on other including broadcasting to multipledie.

According to another embodiment, a number of slug predefinedconfigurations that can be manufactured in large quantities analogous tocurrent mask programmable and to the field programmable technologies.

The depth of some packages exceeds the thickness of a die by factors oftwo to twenty or more. However, by turning the slug on its side, thelength of the slug now corresponds to the side edge of the package.Several layers of package terraces can be used with a terraced slug. Forexample, if the recess of each package terrace is 2 mils and the minimumdie/wafer thickness is 4 mils then multiple terrace levels can beaccommodated.

Major benefits of using terraced slugs to interface to a terracedpackage include savings of at least forty to fifty mils on each sidewhich is very significant in high density packages. Another advantage isthe elimination of the need to wire bond each pad. A further feature isthe elimination of the inductance and capacitance associated with thewire bond which in turn means much faster operation. In addition, thepresent invention provides much better heat conductivity which continuesto be a factor with higher speeds and smaller form factors.

The interconnects of the present invention have numerous applicationsincluding as a Mach-Zender phase shifter which is a typical element thatcould be used to code and decode a photonic signal. Typical digitalspread spectrum direct sequence codes are improved or enhanced byimplementing certain embodiments of the present invention.

Another variation includes having the die inverted wherein the substrateand active elements are on the top and is broadcasting to at least oneother die. The slug can be designed to include any number of variationsthat are all within the scope of the invention.

There are a plethora of available techniques for the interconnect on oneor more of the four sides of a given die. There can be any numbers ofrecesses up to the maximum number of conducting layers for the layers asnot all conducting layers on a given side may be recessed and equippedwith contact pads. There can be any number of contact pads on thedifferent conducting layers up to the maximum permitted by thedimensions of the die, slug, and contacts. Furthermore, different typesof slug contacts, for example, one or more sides could be terraced whileother sides have different contacts while other sides might have nocontacts at all. In addition, the interconnects may involve anycombination involving balls, bumps, rods, and bars on the side and/ortop.

As known to those skilled in the art, there are many types of masks andmasking methods including but not limited to positive, negative, phaseshift, multi-tiered, x-ray, and e-beam.

The mask area represents an area that blocks deposition of material. Anopen area indicates a hole that may be filled, generally with conductingmaterial. The term conducting layer is intended to include but is notlimited to one or more of the permutations of the Damascene method ofinlay which is probably the most widely used method in state-of-the-artfacilities. The term also includes the older method of putting down aconducting layer and then etching it. In one embodiment, the recessesare formed in each successive set of conducting layer and dielectriclayer by masking out the lower layers so that no conducting ordielectric material is deposited.

The present invention has numerous applications and is applicable acrossa number of different fields. One application relates to Edge EmittingLasers (EELs) and Vertical Cavity Surface Emitting Lasers (VCSELs) andthe typical beam dimensions. Note each such device occupies only a verysmall portion of a die edge, for example, 100 to 200 microns or 4 to 8mils, equal to the size of just a single bonding pad or a further sizethat includes the space between it and the next pad. By way ofillustration of one example, approximately 75 such devices can beimplemented on each edge of a die with a 600 mil edge, and the depth issimilarly infinitesimal.

Another application of the present invention relates to techniques forgenerating Photonic Digital Spread Spectrum Signals as is known in theart. By way of illustration, a Mach-Zender phase shifter can be used togenerate the phase coded signals. The ultra-small size of theMach-Zender photonic phase shifter permits many of them to be used inapplications for photonic digital spread spectrum without taking upsignificant space.

The present invention also is applicable to microwave technologies. Forexample, Radio Frequency Identification Devices (RFIDs) long ago provedthat ultra-small antennas could be mounted on chips that containadditional circuitry. As is well known the chips are used inapplications as diverse as credit cards and are embedded in animals,humans, and truck tires. Such devices benefit from the interconnecttechnology detailed herein and is within the scope of the invention.

The ability to communicate with other chips within the package has manybenefits. The present invention provides sufficient isolation whereinsuch chips are used inside packages to send and receive informationbetween and among other chips within the package and perhaps outside thepackage. To keep signals from interfering with each other within a givenpackage and perhaps even off and on the same chip, techniques such asdigital spread spectrum, orthogonal frequency division multiplexing, etccan be used as noted herein.

As noted, one of the applications described herein includes implementingthe sidewards coupling for some of the circuit elements used at themacro level for digital spread spectrum. Another aspect includes theintegration of the coupling technology with the generation of a phasecoded pulse with a tapped delay line. A further application relates tothe non-delay line methods for generating phase coded signals.

Although RFIDs have established ultra-small components and techniquesmade on chips, improvements in higher frequencies are always in demand.As frequencies increase, the resistance also increases for a givenconductor and size, because the skin depth decreases roughly as theinverse square of the frequency. This in turn decreases the conductivityand increases the resistance of the traces, creating an undesirablesituation given that noise margins have significantly also dropped dueto lowered switching thresholds. This again points to the needsdelineated elsewhere to minimize path lengths as much as possible, aproblem addressed by this invention.

Higher dielectric constant materials for transistor gates are now just afew molecules thick with attendant high leakages. The push toward higherand higher frequencies is aided and abetted by a corresponding push forhigher and higher dielectric materials. The present inventionanticipates further advances in the fabrication and manufacturingtechnologies such as higher k materials. Such technological improvementsprovide many benefits such as putting waveguides of different types inthe chip itself at the higher frequencies. By way of further example, ifthe garnets YIG AND YAG and which have k values of 16 and 14respectively were used, the size of a waveguide would decrease by afactor of 4. The length of tapped delay lines would decrease by the sameamount as would the length of ¼ and ½ lambda wavelength stubs. With kfactors of 100, the decreases would be a factor of 10.

In particular but without limiting the scope of the invention thepresent invention allows for a new schema for multiple fanin/fanout andbus access capabilities via the sidewards interconnects. The number ofavailable inputs/outputs is greatly increased facilitating the numberand types of signal communications. Some of the benefits of the presentinvention accomplished by the sidewards coupling as opposed totraversing vertically through numerous layers is increased, speed,decreased power and enhanced noise margins. Other advantages includesimplification of distribution of clock signals, and set/reset signals,including the test capabilities of using in-situ monitoring of selectedsignals.

The present invention permits direct and indirect interconnect, couplingand monitoring using photonic, microwave, and millimeter wave devices,and various combinations thereof. One of the advantages of the presentinvention includes the increased number of inputs/outputs. The terraceddie with conducting layer CL_(N+1) brought out to one side to provideaccess to the contact pads. Typical pad widths currently used are 2 milwith a 2 mil spacing although these dimensions will decrease astechnology improves.

For a typical 600 mil on a side die, this means that on the order of 150such pads can be made per side per conducting layer or about perhaps 600per conducting layer. Eight conducting layers allow roughly 4800inputs/outputs per die compared to the current 1800 to 2000 currentlyavailable with conventional BGA and roughly 400 to perhaps 600 withconventional wire bonding. Larger numbers of conducting layers and orsmaller contact pad sizes will increase this even further.

There are significant advantages to the sidewards coupling and decreasedline lengths. It is well known that transistor switching times havedecreased so much that propagation delays and connectivity often faroutweigh them. As stated previously, traversing many layers ofinterconnect with the attendant numbers of vias and increased pathlengths has several drawbacks compared to the present invention. Longerpath lengths slow the circuit down not just because of the longer pathlengths but also because of the parasitic capacitances of the highlydense signal traces. Moreover, as the line widths decrease, the numberof “squares” increases for a given length of line which in turnincreases the amount of resistance for a given length of line.Exacerbating these problems is that the effective thickness decreases asoperating frequencies increase due to skin depth decreases which furtherincreases the resistance of a square with a concomitant increase in lineresistance.

This also increases the resistance of a given square making it moredifficult to design clock set/reset trees and other busses whoseelements must track and whose skews must be minimized. The increasedpath lengths also use more power because of the higher overallresistance of the line have greater voltage drops which significantlyimpair noise margins especially in the era of large chip sizes and lowvoltages. It is well known that the clock on a chip takes upconsiderable chip area and uses considerable power. Often not realizedare the problems of dealing with slave clock skews and concomitantsetup/hold and slack time issues. All of these problems aresignificantly exacerbated by the inability to connect directly from theconducting layer of one die to that of another die. Many chips havephase locked loops (PLLs) to synchronize the incoming data which placeadditional restrictions and which are impacted by the aforementioneddelays and fanout restrictions of the current art.

A further benefit of the above scheme is that it allows newernon-contact probe sensing methods to examine the signals on the chipin-situ and while the chip is operating. For example testing outputsfrom any of the scan methods such as LSSD (Level Sensitive Scan Design)can be sent to on chip photonic, microwave, and/or millimeter wavedevices for transmittal to outside contacts as described herein.

There are currently several ways of separating individual die fromwafers. The most common methods are by scribing and dicing as known tothose skilled in the art. The depth of the cut of current dicing sawscan be controlled to a precision of one micron. However, it should bereadily apparent that the present invention is not restricted to suchwafer technology.

Several different methods of interconnecting signals to/from the side ofone die to/from the sides of adjacent dies are provided herein. Theresulting combinations are mounted on substrates and/or in packagesusing standard techniques.

It is well known that a significant portion of the power dissipated by adie is removed via the contacts. A majority of the heat is generated bythe active elements such as transistors and diodes. The conductinglayers are above the layers containing the active elements. As thenumber of conducting layers has sharply increased, the heat generatingmechanisms are buried further and further away from the means to get ridof the heat.

As the side connections of the present invention have much lowerresistance, capacitance and inductance per square, they are useful forinterconnections on any die regardless of whether they go to other diewithin the package. In one embodiment the side connections are used toroute a signal which fans out to several different elements on the diewhich are widely separated and thus solve routing problems. This can beimportant in the struggle to route slave clocks and reset signals whoseskews and slack times must track each other and be minimized.

As detailed herein, it should be readily apparent that “hard” wired(direct connection), “soft” wired (capacitive and/or inductive coupling)and/or the use of conductive elastomers and wireless techniques all havevalue in interconnecting multiple chips in a package. The presentinvention allows for interconnects using any of these techniques eitherseparately and/or simultaneously.

Wireless techniques, as described herein, includes photoniccommunications, microwave communications, millimeter wave combinationsor a combination thereof wherein the indirect coupling can also beachieved by capacitive and/or inductive coupling at short ranges amongthe chips in the package, especially those in apposition to one another.Within these wireless categories are various communication methodologiesas known to those skilled in the art.

By way of illustration, one particular type of digital spread spectrumis described herein for exemplary purposes, however it should be readilyapparent that many other types are possible and all are within the scopeof the present invention. The present invention does not require orapply to just one specific technology, methodology, or structure.

Note that photonic, microwave, millimeter wave signals can all bepresent simultaneously because of the different wavelengths and/orcoding. Moreover, using digital spread spectrum technique, differentcodes and/or different frequencies from multiple sources of each typecan be present simultaneously.

A further application includes memory and stacked multi-chip memorypackages. Speed and latency are two very major concerns of not justmemories but also many other types of chips. For example, it is withinthe scope of the invention to have special ultra-thin die 40 micronthick which are separated and supported by 40 micron thick interposerswith an additional 40 micron allocated to wire loop for bonding.

The term “wireless” has come to imply a digital bit stream that issuperposed on a microwave or photonic carrier which is then removed tobe decoded in a non-co-located receiver. In the context herein in whichthe communication is among chips separated by almost infinitesimaldistances, it may or may not be necessary to convert to and frommicrowave frequencies although such conversions are within the scope ofthe invention. Instead the digital bit stream may be transmitteddirectly across the infinitesimal distances among chips.

There is a benefit to higher speed communications because the higheroperating frequencies enable structures such as various, smallerantennas, and various types of waveguides using modes other than theTE10 modes. Normally useless evanescent modes may have benefit in thisapplication. Systems running at 40 GHz are currently available andlikely to increase. When communication is desired with chips in the samepackage that are not adjacent to each other or for other reasons, thesignal may be superposed on a microwave or photonic carrier.Communications of 40 GHz may utilize standard techniques such as phaselocked loops albeit at higher frequencies than that at which they arecommonly used.

When communication is desired among chips that are not adjacent to eachother in the package and sometimes with those that are adjacent to oneanother, it may be desirable to use a wireless technique to enable suchcommunication.

Such a method should also enable many such communications among thedifferent chips in the package to take place simultaneously and withoutinterfering with one another and without the need for direct contactwhen the proper wireless techniques are usable.

Digital spread spectrum techniques as well as other methods as detailedherein can be used for such communications. They also have considerablevalue when the direct contacts in this invention are used among chips inthat they mitigate the undesirable cross-coupling of signals on the chipat superhigh frequencies of operation which in turn force the greaterspacing among chip lines.

The digital spread spectrum and similar techniques can enable thecommunication infrastructure. Digital spread spectrum is thus a means ofenabling the pieces of multiple signals to occupy parts of the samespectrum without interfering with one another. Digital spread spectrumis well-known and numerous digital spread spectrum codes have beendeveloped as is known in the art.

Originally there were two generic types of digital spread spectrum,namely frequency hopping and direct sequence. A newer technique isOrthogonal Frequency Division Multiplexing called Orthogonal WavelengthDivision Multiplexing when photonics are used.

In direct sequence digital spread applications, the phase of the signalis changed by 180 degrees if the signal is a “one” or not changed if thesignal is a “zero.” Opposite coding as well as other phases, e.g., 90 oreven 45 or 22.5 degrees have also been used. The signal can also becoded photonically. If inner and outer codes are used, the inner code iscalled the “bit” or more commonly the “chip.” The power density in anypiece of the spectrum of a given direct sequence signal is typicallyvery low. The correlation gain of the direct sequence signal is achievedby reassembling the pieces according to the code that was employed.

As noted although the current invention does not require the use ofdigital spread spectrum or the sequences however the packagingtechniques described herein are a significant enhancement to the directsequence applications.

Automated layout tools such as silicon compilers have been availablefrom a number of major vendors for a number of years and are generallypart of standard layout packages. These tools enable the form factor,pitch and aspect ratio, of a given die or portion of a die to be readilychanged. As the number of pins in IC's increase and with the need tokeep these packages small, the spacing between package pins decreases.Since these arrays can have hundreds of pins on each side and because ICdesign rules have minimum trace widths and clearances, many IC signallayers are required to be able to interconnect to the pins of thepackage. IC designers assure compliance with Design Rules with softwaretools that has rules for clearances between various object pairings, andconformity of a given layout. The software tools confirm that a givenpattern complies with any requirement, criterion, or preferencearticulated.

As noted herein, one of the many advantages of the present invention isthe ability to interconnect die of radically different thicknesses andtherefore enable technologies which are optimum for a given function tobe used, mixed, and interconnected in the same package. For example,HBTs are generally the technology of choice for analog-to-digital (A/D)converters, low phase noise amplifiers, and photonic elements such asEdge Emitting Lasers. On the other hand Si CMOS is generally thetechnology and structure of choice for most other applications becauseof low cost.

In addition, there are a number of related designer issues that requiredetailed knowledge and forethought. For example, the designers generallyestablish design plans for the chip “real estate” and layout. They alsoconsider how to avoid losing the gains obtained on the chip in thepackage when the signals go to the outside world which has capacitancesand inductances which are orders of magnitude greater than those withinthe chip or within multiple dies connected to each other within a givenpackage. The designers also contemplate how to obtain as muchfunctionality as possible among elements that are symbiotic, for exampledifferent in some respects (e.g.: analog, digital, microwave, orphotonic) but complementary in other aspects. These designers also dealwith the gate-to-pin ratio and the larger and larger numbers of I/O.Further designer considerations include how to realistically model andsimulate the interconnects that travel circuitous paths, such as fromthe bottom of the conducting layer stack to the top. Even furtherconsiderations include wired functions (e.g.: NAND, NOR, AND, and OR)along the paths that can go up to a given layer and then reverse andcome part way back down to pick up another wired function as allowed bythe structure and technology, including CMOS and differential cascode,Source Coupled FET Logic (SCFL), and Emitter Coupled Logic (ECL).

As noted herein, the industry is pushing for higher speeds and smallerpackaging, including die packaging. The industry continues to evolve andthere is an increasing push to merge and integrate symbiotic structures,including ADCs, DACs, analog and digital microwave/millimeter wave, andphotonic devices including Edge Emitting Lasers on a single chip. Theincreased use of HBTs made from different materials such as SiGe,GaAs/AlGaAs, InP, SiC, and SiN, and the newer InSb has certain distinctadvantages which enables this merging.

A major benefit of the HBT is the transconductance, a measure of theability to drive loads both on and off-chip, which is one to threeorders of magnitude greater than that of a FET device including thecommon CMOS structures. The increased usage of custom designs configuredto a specific function, for example Fast Fourier Transforms (FFT) andAnalog-to-Digital Converters (ADC), and characterized as commodities,continue to mitigate the expense and chip development. There has been agrowing tendency of some manufacturers to use smaller specialized chipswith one or more functions which must be integrated with other chips.Generally this occurs when the number, type, and speed of pinouts andother parameters are not dominant issues. A number of central processingunits now carry ‘on-chip’ wireless communication capabilities tofacilitate such communications. One of the reasons for the developmentof such chips comes from a number of trends such as the ‘point andclick’ nature of the internet and the instantaneous nature of voice andgraphics communications.

There have also been some recent developments and trends related to theincreasing use of digital spread spectrum and analog spread spectrumtechniques in consumer applications. The development of materials withhigh dielectric constants is used to increase the number and variety ofshort range communication techniques in small packages. There are alsoemerging areas for some methods for ultra-short range coupling such ason a die.

As noted herein, the present invention can be integrated with carbonnanotubes and have features sizes as low as one one-hundredth of that ofcurrent semi-conductors with extremely high electrical conductivities,thermal conductivities twice that of diamond which has the highest ofall conventional materials, and the capability of being grown atpredefined sites on silicon wafers. Micro Electro-mechanical Machines(MEMS) is another area that will pioneer new systems and devices in manyareas. Single nanocrystal technology and the development of siliconlasers using single silicon nanocrystal technology is another area thatcan employ the technology. Heretofore injection, i.e., semi-conductorlasers had to be fabricated using double heterojunction bipolartransistors (HBTs) which is a more difficult process. Quasicrystallinestructures may enable communication systems to be powered by photonsinstead of electricity and enables light to make sharp turns as ittravels through photonic circuits unlike current photonic circuits.These new developments may significantly increase the speeds ofcommunications and computing devices. Furthermore, faster and moreaccurate “steering” to a specific address on another chip in the packageor even to a different part of the same chip must be achieved.

The crowding of the radio spectrum and the increasing value of usingphotonics for both processing and interconnect has also highlightedcertain limitations of the current state of the art. The movement tohigher and higher frequencies is a problem on the chip because it forcesa minimum spacing between parallel adjacent lines and/or a maximumoperating frequency. It is also a problem because as frequencyincreases, the skin depth decreases which means that long runs thattraverse many conduction and attendant dielectric layers will havehigher resistance especially when the resistance of the stepped vias istaken into account.

The present invention includes numerous novel embodiments, such ascommunicating within a package using active elements and wirelesstechniques including photonic devices, microwave, millimeter wave,slugs, active element slugs, and programmable slugs, terraced die andslugs, interconnection of die having varied shapes, sizes andthicknesses, inductive coupling for interconnections of die to die anddie to slugs.

A number of architectures employing the side mounting of theinterconnects are within the scope of the present invention. Thefeatures and advantages described herein are not all-inclusive and, inparticular, many additional features and advantages will be apparent toone of ordinary skill in the art in view of the drawings, specification,and claims. Moreover, it should be noted that the language used in thespecification has been principally selected for readability andinstructional purposes, and not to limit the scope of the inventivesubject matter.

The foregoing description of the embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. Many modifications and variations are possible in light ofthis disclosure. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto.

The invention claimed is:
 1. A method for forming a die, the methodcomprising: forming a conducting layer; forming a plurality ofinterposed conducting layers separated by a plurality of interposeddielectric layers, wherein the plurality of interposed conducting layersand the plurality of interposed dielectric layers are interposed betweenthe conducting layer and a top surface of the die; and forming a contactpad electrically connected by an electrical connection to one of theplurality of conducting layers and extending to a lateral edge of thedie, wherein: the electrical connection does not traverse all of theplurality of interposed conducting layers and all of the plurality ofinterposed dielectric layers; and the contact pad comprises a taperedcontact pad.
 2. The method of claim 1, wherein said forming a contactpad comprises forming a stepped via.
 3. The method of claim 2, whereinsaid forming a stepped via comprises: forming hole in a dielectriclayer; and filling the hole with a conductive material to form a part ofthe stepped via.
 4. The method of claim 3, wherein the conductivematerial comprises copper.
 5. The method of claim 3, wherein theconductive material comprises a refractory metal.
 6. The method of claim3, wherein said filling the hole with a conductive material is performedwhen an abutting conductive layer is formed.
 7. The method of claim 2,wherein said forming a stepped via comprises: forming a plurality ofholes in a corresponding plurality of dielectric layers; and fillingeach of the plurality of holes with a conductive material to form a partof the stepped via.
 8. The method of claim 7, wherein the conductivematerial comprises copper.
 9. The method of claim 7, wherein theconductive material comprises a refractory metal.
 10. The method ofclaim 7, wherein each of the plurality of holes is filled with aconductive material when an abutting conductive layer is formed.
 11. Themethod of claim 7, wherein a portion of the plurality of holes are sizeddifferently from each other.
 12. The method of claim 11, wherein theportion of the plurality of holes are sized differently from each otherto contribute to a formation a flange in the tapered contact.
 13. Themethod of claim 2, wherein said forming a stepped via comprises: forminga plurality of stepped via conducting layer portions; and forming aplurality of stepped via dielectric layer portions.
 14. The method ofclaim 1, wherein the contact pad comprises an input/output (“I/O”) pad.